Nuclear magnetic resonance absorption has been conventionally used as means for analyzing chemical substances and clarifying reaction processes. In recent years, nuclear magnetic resonance absorption has become the object of public attention in a variety of medical fields through NMR zeugmatography or the like for observing the distribution of components of tissue of a living body.
For example, it is common practice in order to make clear transplant adaptability of an internal organ, energy metabolism or the like, to conduct an NMR measurement test on an internal organ, a muscle or the like of an experimental animal under cultivation in a perfusion solution. More specifically, an internal organ of a living thing disposed in a perfusion cell is placed in a static magnetic field, and a free decay signal (free induction signal) obtained by applying a rotating magnetic field in the form of a pulse is measured by a receiver coil disposed around the cell. The free induction signal is analyzed to obtain an NMR spectrum. Based on the NMR spectrum thus obtained, it is possible to clarify the condition of phosphorus atoms contained in phosphorus compounds such as creatinic acid, ATP, inorganic phosphoric acid and the like. Thus, the transplant adaptability of the internal organ may be judged.
FIG. 9 shows the arrangement of a conventional measuring apparatus. In FIG. 9, an internal organ or the like of a small animal is put in a cell 22 around which a receiver coil 21 is wound and which is perfused with a perfusion solution (a physiological saline solution or the like). With a static magnetic field H applied to the receiver coil 21 at a right angle to the axis thereof, a free induction signal generated in the receiver coil 21 is detected.
According to this apparatus, an NMR measurement may be carried out for a long period of time while the perfusion solution prevents the internal organ or muscle from being dried.
However, when the concentration of the perfusion solution is changed with the passage of time and the corresponding changes in the absorption spectrum with the passage of time are to be analyzed, the above-mentioned arrangement presents the following problem.
The perfusion solution flows in the receiver coil. Accordingly, when carrying out a measurement with a changing concentration of the perfusion solution the inductance of the receiver coil is changed according to the changes in concentration of the perfusion solution. This assures neither tuning of, the receiver coil, nor matching of the impedance and not only changes the appearing position of the absorption spectrum, but also weakens the absorption spectral line, causing this line to be embedded in noise. Thus, no accurate measurement may be carried out.
In this connection, perfusion solutions having different concentrations are conventionally prepared, and each time each perfusion solution flows, the tuning of the receiver coil is done over again and measurement is then carried out. This not only makes the measurement troublesome, but also fails to acquire the data corresponding to continuous changes in concentration.
Further, in the above-mentioned arrangement, even though the cell is made in a large size and a large-size internal organ is housed therein, the current art may provide only a small area presenting a uniform static magnetic field. This causes the internal organ to partially protrude from the uniform magnetic field, thereby to disadvantageously deteriorate the resolution of an NMR spectral signal obtained by analyzing the free induction signal.
It is an object of the present invention to provide NMR measuring method and apparatus for tissue of a living body, capable of acquiring a highly sensitive measurement signal even though the measurement is made with concentration of a perfusion solution and capable of also measuring also a large-size internal organ.